1. Field of the Invention
This invention broadly relates to a method and apparatus for the extrusion of wood chips, shavings or sawdust to produce a refined product having a multitude of separated fibers of relatively long lengths and narrow cross-section. More particularly, the invention is concerned with an extruder head and screw each having bar-like restriction elements extending transversely across the grooves between flighting, and the bars interact in a scissors-like fashion to roll and twist the fibers apart without excessive transverse severing of the same. A final, conical section of the extruder screw has two juxtaposed grooves each presenting three processing zones which each include a compression region, a restricted region and a decompression region sequentially arranged along the length of the grooves and upstream of an annular outlet, in order to choke the flow of wood through the extruder and roll the wood particles against each other without the use of a die at the outlet of the extruder. The extrudate is of a flowable nature which can be easily storaged, conveyed, or handled. Additionally, the extrudate is highly desirable for use in the production of a special core for particle board, since the relatively thin fibers may be readily and efficiently coated to a smooth finish after the board is cut, while the long lengths of the fibers interconnect to form a stronger composite board product than would otherwise be possible.
2. Description of the Prior Art
The use of particle board for furniture, cabinets and other types of finished construction projects has significantly increased in recent years. Particle board has in many instances replaced plywood due to the improved dimensional stability of particle board and the lower cost of the same. In most cases, particle board is comprised of relatively flat, small chips that are bonded together by an adhesive such as epoxy resin.
However, particle board tends to have relatively large voids and pores between the chips because the latter, during manufacture of the board, resist compression to a dense, tightly packed condition. As a result, sawn or cut edges of the board present a number of voids and cavities which, for the most part, cannot be readily coated to a smooth finish. Consequently, the cut edges of the particle board when used in furniture, cabinets and the like are normally trimmed with a piece of natural wood of a type selected to match the desired finish to be applied to the faces of the board and other components of the finished structure. As can be appreciated, the usual practice of selecting, cutting and affixing a trim strip to the sawn edges of particle board significantly increases the overall cost of the finished product as well as the time expended in construction of the same.
Other types of composition board, and particularly those products known as fiber board, have been manufactured by processing shavings, wood chips or sawdust in a disc refiner or pressurized refiner and then applying an adhesive and pressing the refined fibers together in order to form the resultant board product. The core of fiber board, being comprised of tightly compacted, small fibers, presents a relatively smooth edge when sawn due to the small size of the voids between adjacent fibers, in contrast to the larger voids presented along the cut edge of particle board. Unfortunately, fiber board is relatively expensive, due in part to high energy costs which are associated with operation of the disc refiner or pressurized refiner, the latter of which requires significant amounts of steam energy.
Hence, it would be a desirable advance in the art if means were provided to refine wood chips, shavings or sawdust into a product that is characterized as having thin, at least partially separated fibers each of a relatively long length, but with significantly reduced costs for energy in comparison to the operating expenses associated with the use of disc refiners and pressurized refiners. Advantageously, such a refined product could be utilized in the manufacture of a special core for particle board, so that cut edges of the same can be easily coated to present a smooth, finished appearance that matches the face of the boards or other components of the finished article.